Electrode structure of el device

ABSTRACT

An array of OLEDs is provided. The array includes a first electrode that has a plurality of physically separate pieces that are electrically connected by a bus line. The array further includes a second electrode, and an organic layer disposed between the first and second electrodes. The organic layer is electrically connected to the second electrode, and to at least one of the physically separate pieces of the first electrode. The embodiment may be used to fabricate an array of OLEDs on a flexible substrate.

The subject matter of this application is related to concurrentlypending patent application Ser. Nos. 09/802,976 and 09/802,977, whichare incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor fabrication,and more particularly to the use of a bus line in devices fabricated ona flexible substrate.

BACKGROUND OF THE INVENTION

Organic light emitting devices (OLEDs), which make use of thin filmsthat emit light when excited by electric current, are becoming anincreasingly popular technology for applications such as flat paneldisplays. Popular OLED configurations include double heterostructure,single heterostructure, and single layer, and a wide variety of organicmaterials, some of which are described in U.S. Pat. No. 5,707,745, whichis incorporated herein by reference. As used herein, the term “organicmaterial” includes polymers as wells as small molecule materials thatmay be used to fabricate OLEDs.

Flat panel displays typically include an array of picture elements, orpixels, deposited and patterned on a substrate. Such a pixel array istypically a matrix of rows and columns. In an OLED display, each OLEDpixel includes an organic light emitting diode that is situated at theintersection of each column and row line. The first OLED displays, likethe first LCD (Liquid Crystal Displays), have typically been addressedas a passive matrix (PM) display. This means that to cause a particularpixel to luminesce, electrical signals are applied to the row and columnlines of that particular pixel. The more current that is pumped througheach pixel diode, the brighter the pixel appears visually. One method ofproviding grayscale to the display is to vary the current level of thepixel.

In practice, a voltage is applied to a single row line, and a path forcurrent flow is selectively provided at individual columns. Thisprovides current flow through selected pixels on the single row, thusallowing current to flow causing each pixel in that row line toluminesce at the desired brightness. The next row line is thenaddressed, and once again, all the pixels on that row line are energizedto produce the required brightness. The display continuously scans allthe row lines sequentially, typically completing at least 60 scans ofthe overall display each second. In this way, flicker is not seen sincethe display is addressed fast enough, for typical observationconditions, that the pixels cannot be seen to be continuously turning onand off Preferably, the magnitude of current flow through each columncan be controlled, such that the brightness of the pixels can becontrolled.

For OLEDs from which the light emission is only out of the bottom of thedevice, that is, only through the substrate side of the device, atransparent anode material such as indium tin oxide (ITO) may be used asthe bottom electrode. Since the top electrode of such a device does notneed to be transparent, such a top electrode, which is typically acathode, may be comprised of a thick and reflective metal layer having ahigh electrical conductivity. In contrast, for transparent ortop-emitting OLEDs, a transparent cathode such as disclosed in U.S. Pat.Nos. 5,703,436 and 5,707,745 may be used. As distinct from a transparentor bottom-emitting OLED, a top-emitting OLED is one which may have anopaque and/or reflective substrate, such that light is produced only outof the top of the device and not through the substrate, or can be afully transparent OLED that may emit from both the top and the bottom.

The transparent cathode that is used in such a transparent ortop-emitting device preferably has optical transmission characteristicssuch that the OLED has an optical transmission of at least about 50%,although lower optical transmissions may be used. More preferably, thetransparent cathode has optical transmission characteristics that permitthe OLED to have an optical transmission of at least about 70%, stillmore preferably, at least about 85%. These requirements placesignificant limitations on the materials and thicknesses of thetransparent cathode.

The transparent cathodes as disclosed in U.S. Pat. Nos. 5,703,436 and5,707,745 typically comprise a thin layer of metal such as Mg:Ag with athickness, for example, that is less than about 100 angstroms. The Mg:Aglayer is coated with a transparent, electrically-conductive,sputter-deposited, ITO layer. Such cathodes may be referred to ascompound cathodes or as TOLED (“Transparent-OLED”) cathodes. Thethickness of the Mg:Ag and ITO layers in such compound cathodes may eachbe adjusted to produce the desired combination of both high opticaltransmission and high electrical conductivity, for example, anelectrical conductivity as reflected by an overall cathode resistivityof about 30-100 Ω/□ (ohms per square). However, even though such arelatively low resistivity may be acceptable for certain types ofapplications, such a resistivity may still be somewhat too high for apassive matrix array of OLED pixels in which the current that powerseach pixel needs to be conducted across the entire array through thenarrow strips of the compound cathode.

It is expected that new materials may be developed that can be used astransparent electrodes having resistivities less than 30 ohms persquare, and that the present invention may be used in conjunction withsuch materials. Also, resistivities greater than 100 ohms per square maybe acceptable for some applications, and the present invention may alsobe used in such applications.

It is known to use bus lines to mitigate limitations on the electricalconductivity of a transparent electrode. In the context of a passivematrix array of OLEDs, the bus line is a thick electrically conductivestrip that runs parallel to a transparent electrode, and which provideselectrical conductivity in the direction of the electrode. For example,U.S. Pat. No. 6,016,033 to Jones et al. discloses the use of a bus linein an array of OLEDs. Because the bus line is made of a thickelectrically conductive material, it does not transmit light, andunfavorably results in an inactive area on the array of OLEDs. Becauseit is desirable to maximize the active area of an OLED display, it isdesirable to minimize the area of the bus line. The active area may bequantified by a “fill-factor,” which is the percentage of the area of anarray that is active or that emits light. Because of the enhancedelectrical conductivity that is provided by a bus line, a bus line maybe used notwithstanding the disadvantageous inactive area.

The organic materials of an OLED are very sensitive, and may be damagedby conventional semiconductor processing. For example, any exposure tohigh temperature or chemical processing may damage the organic layersand adversely affect device reliability. As a result, the processesconventionally used to fabricate a thick metal feature such as a busline may damage any organic layers that are already present.

One technique that may be used to protect the delicate organic layers ofan OLED is an integrated mask through which layers may be selectivelydeposited during fabrication. The mask is “integrated” because it isleft in place after fabrication, thus being integrated into the finaldevice. Using an integrated mask is particularly desirable where thesteps used to pattern material or to remove a mask have the potential todamage the device. Even where the integrated mask does not cover thedelicate organic layers, the integrated mask protects the delicateorganic layers by providing a patterning mechanism that does not requirethe patterning or removal of a mask once the organic layers are inplace, i.e., the potentially damaging processes used to form theintegrated mask are performed before the organic layers are present, andthe potentially damaging processes used to remove a mask are notperformed at all because the integrated mask is left in place. It isknown to use an integrated mask to fabricate the top electrodes of anarray of OLEDs, as disclosed in U.S. Pat. No. 5,701,055 to Nagayama et.al.

One problem that has been observed with conventional integrated masks isthe shorting of adjacent electrode layers across the mask. It is knownto use integrated masks having an overhang to mitigate shorting acrossthe mask, as disclosed in U.S. Pat. No. 5,701,055 to Nagayama et. al.However, even with a conventional overhang, the process used to depositthe electrode must meet certain criteria to avoid shorting problems.

First, in order to avoid shorting problems, the “footprint” of thedeposited material, defined as the surface area onto which significantmaterial is deposited, should be sharply limited to those surfaceshaving a direct line of sight, unobstructed by the mask, to the sourceof material being deposited. The footprint should not extend ontosurfaces that do not have a direct line of sight to the source ofdeposited material. Whether deposition is limited in this way isdependent upon the deposition process. Processes such as low energydeposition of metals by thermal evaporation, generally result infootprint relatively sharply limited to surfaces having a direct line ofsight to the source of material. In contrast, processes such as chemicalvapor deposition may result in a significantly larger footprint, suchthat there is significant deposition onto surfaces not having a directline of sight to the source of material. Processes such as sputterdepositing have a footprint between that of thermal evaporation and thatof chemical vapor deposition. One mechanism that may lead to a largerfootprint is collisions between atoms or molecules of the material beingdeposited during transit to the substrate, and the resultant scattering.A low “sticking efficiency” of the atoms or molecules being deposited isanother such mechanism. These mechanisms may lead to the side walls of aconventional integrated mask being coated with substantial quantities ofthe material being deposited even though such surfaces may not be withina direct line of sight from the source material.

Second, in order to avoid shorting problems, deposition that issignificantly off-axis should be avoided, even for processes that have alimited footprint. Off-axis deposition is deposition from an angle notperpendicular to the substrate. Off-axis deposition may result insurfaces losing their protection from a direct line of sight to thesource of material being deposited, such that material may be depositedinto the recessed area under an overhang. Moreover, off-axis depositionoften involves deposition from a variety of different angles, such thateven more surface area loses protection from a direct line of sightduring the process. Off-axis deposition may occur for many reasons. Forexample, the geometry of the substrate, the source, and their relativelocations may lead to significant off-axis deposition, and may even leadto significant variations in the angle of deposition at different pointson the substrate. The substrate may be placed on a moving conveyor beltduring deposition, which inherently leads to off-axis deposition whenthe substrate is not directly beneath the source of material, and maylead to very large angle off-axis deposition when the substrate is atthe edge of the deposition chamber. The substrate may also be rotatedduring deposition. Even processes that have a somewhat limitedfootprint, such as sputter depositing, may lead to shorting if there issignificant off-axis deposition. It is believed that sputter depositingthrough a conventional integrated mask leads to shorting when off-axisdeposition from angles of about 30 degrees or greater is present,although there may be shorting at smaller angles depending upon theexact process parameters.

It may be desirable, or even necessary in some cases, to use processeshaving a large footprint, and/or off-axis deposition, to fabricatecertain types of layers that are used in an OLED. However, suchprocesses may cause deposition to occur in undesirable regions of thedevice. For example, an ITO layer typically needs to be deposited usinga high energy vacuum sputtering process that produces substantialscattering. Thus, using conventional integrated masks, it may not bepossible to fabricate desirable but previously unattainable structuressuch as transparent or top-emitting OLEDs using a compound Mg:Ag/ITOcathode in a passive matrix OLED array. The use of such a conventionalmask may result in the ITO layer causing harmful shorting acrossadjacent compound cathode strips.

FIG. 1 (prior art) illustrates the type of shorting of an electrodelayer that may occur across an integrated mask due to the use of adeposition process that is not perfectly unidirectional. Mask 110 isfabricated on top of substrate 100. A metal layer 120 is deposited overmask 110, with the goal of fabricating electrodes 120 a and 120 b thatare electrically separated. If the vapor deposition process is highlyunidirectional, electrodes 120 a and 120 b, and residual layer 120 d,are deposited. Any residual layer 120 c that forms would not becontinuous or thick enough to have significant electrical conductivity,because the vapor deposition process is highly unidirectional and thereis no direct line of sight between the metal deposition source andresidual layer 120 c. However, if the vapor deposition process producestoo much scattering and is, thus, insufficiently unidirectional,residual layer 120 c may be continuous and have significant electricalconductivity. In this case, residual layers 120 c and 120 d may form ashort between electrodes 120 a and 120 b.

It would be desirable to be able to fabricate transparent ortop-emitting OLEDs that exploit the high optical transmission ofcompound cathodes, such as Mg:Ag/ITO, in a passive matrix display, butwithout having such devices limited by the lower electrical conductivityof such compound cathodes. Furthermore, it would be desirable to be ableto vapor deposit electrically conductive materials without encounteringthe shorting problems that may be experienced whenever such electricallyconductive materials undergo substantial scattering during thedeposition process.

OLED technology offers the potential to be highly functional and durablein a flexible format. OLEDs fabricated on flexible substrates may offerseveral advantages over OLEDs fabricated on conventional substrates,such as glass. These potential advantages include impact resistance,light weight, thinness, in-use flexibility and conformability. FlexibleOLEDs are discussed in more detail in Weaver et al., “Flexible OrganicLED Displays,” 2001 Soc. Vac. Coaters 505/856-7188, 44th AnnualTechnical Conf Proc. (2001) ISSN 0737-5921 (“Weaver et al.”), which isincorporated by reference in its entirety.

However, due to the limitations on the materials and thicknesses ofconventional electrodes used in OLEDs, such electrodes may not bewell-suited for use in OLEDs fabricated on a flexible substrate. Inparticular, the flexing of the substrate may cause such electrodes tocrack, delaminate, or otherwise sustain damage that could adverselyaffect reliability. It would be desirable to achieve electrodes thatcould be reliably used on OLEDs fabricated on a flexible substrate.

SUMMARY OF THE INVENTION

In an embodiment of the invention, an organic light emitting device isprovided. The device has a first electrode, an insulating strip disposedover a portion of the first electrode, and a bus line disposed on top ofthe insulating strip, such that the bus line is electrically insulatedfrom the first electrode by the insulating strip. An integrated mask isdisposed over the bus line, such that a portion of the bus line remainsexposed vis-a-vis the insulating strip and the integrated mask. Anorganic layer is disposed over the first electrode, such that theorganic layer is electrically connected to the first electrode. A secondelectrode is disposed over the organic layer, such that the secondelectrode is electrically connected to the organic layer, and such thatthe second electrode is electrically connected to the exposed portion ofthe bus line. A method of fabricating the device is also provided, whichinvolves depositing the organic layer and the second electrode throughthe integrated mask, such that the second electrode is in electricalcontact with the bus line.

The bus line may be disposed completely under the recessed area andcompletely under the overhang on one side of the base such that none ofthe bus line contributes to a loss in the fill factor of the OLED array.The recessed area on at least one side of the base has an aspect ratiosufficiently large such that no vapor deposition may occur in thefurthermost interior, distal, depths of the recessed area even whenhighly scattered materials are vapor deposited. However, the outermost,proximal, exposed portion of the bus line is sufficiently close to theoutermost extension of the overhang so as to allow vapor deposition of ahighly scattered second electrode material to make electrical contactwith at least a proximal portion of the exposed portion of the bus line.

In an embodiment of the invention, a photoresist mask is provided,having a central region fabricated on an underlying layer. An overhangsupported by the central region is separated from the underlying layerby a recessed area. The recessed area has an aspect ratio of at leastabout 1.5. The mask may be advantageously used to pattern electrodesdeposited through the mask by chemical vapor deposition or sputtering,such that there is no significant conductivity across the mask betweenthe patterned electrodes.

In an embodiment of the invention, an array of OLEDs is provided. Thearray includes a first electrode that has a plurality of physicallyseparate pieces that are electrically connected by a bus line. The arrayfurther includes a second electrode, and an organic layer disposedbetween the first and second electrodes. The organic layer iselectrically connected to the second electrode, and to at least one ofthe physically separate pieces of the first electrode. The embodimentmay be used to fabricate an array of OLEDs on a flexible substrate.

In an embodiment of the invention, an electrode having a plurality ofphysically separate pieces is provided. A bus line electrically connectsthe plurality of physically separate pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) illustrates the shorting of an electrode layer acrossan integrated mask due to the use of a deposition process that is notperfectly unidirectional.

FIG. 2 shows an cross-sectional illustration of a mask in accordancewith an embodiment of the invention.

FIG. 3 shows a cross-sectional photograph of an actual mask fabricatedin accordance with the present invention, similar to the maskschematically illustrated in FIG. 2.

FIG. 4 shows a cross sectional illustration of a device incorporating anintegrated mask in accordance with an embodiment of the presentinvention.

FIG. 5 shows the device of FIG. 4 from a top view.

FIG. 6 shows a cross section of an OLED having a barrier layer.

FIG. 7 (prior art) shows a top view of a schematic diagram of a passivematrix display.

FIG. 8 shows a top view of electrodes having physically separate pieces,where the electrode spans a substrate in one direction.

FIG. 9 (prior art) shows a top view of a large, physically contiguouselectrode fabricated on a substrate.

FIG. 10 shows a top view of an electrode that covers most of asubstrate, where the electrode includes physically separate pieces.

FIG. 11 shows a top view of a physically contiguous electrode thatcovers most of a substrate, where bus lines running in two directionselectrically connect various regions of the electrode.

FIG. 12 shows a top view of physically contiguous electrodes that spanthe length of a substrate in one direction, but are relatively narrow inthe other direction, where bus lines running parallel to the electrodeselectrically connect various regions of the electrodes.

FIG. 13 shows an electrode similar to the electrode of FIG. 10, andshows devices that each incorporate several of the physically separatepieces of the electrode.

FIG. 14 shows an electrode similar to the electrode of FIG. 10, andshows multiple devices sharing a single physically separate piece of anelectrode.

DETAILED DESCRIPTION

The present invention will be described with reference to theillustrative embodiments in the following processes and drawing figures.

One embodiment of the present invention provides a photoresist maskhaving an overhang larger than those available in the prior art. Thislarge overhang enables the use of processes that were not previouslyavailable, such as depositing electrodes through an integrated maskusing chemical vapor deposition (CVD), or using sputter deposition withsignificant off-axis deposition. For example, this embodiment may enablethe use of sputter deposition where there is off-angle deposition fromangles greater than 30 degrees—angles up to 45 degrees, 60 degrees, oreven approaching 90 degrees. These electrodes may be transparent if theyare made of the appropriate materials, such as indium tin oxide (ITO),MgAg, aluminum, or Al:LiF, fabricated to the appropriate thickness.

The large overhang may also enhance the yield of processes that arepresently practiced with conventional masks, and allow such processes tobe reliably used with less a stringent controls. In addition, evenhighly directional deposition processes generally have an angle ofdeposition that varies significantly over a few centimeters. Anintegrated mask with a large overhang may be used to increase the areaover which processes sensitive to angle of deposition is important, suchas processes previously practices with shadow masks or integrated maskswith smaller overhangs.

Preferably, the mask is monolithic, where monolithic means that the maskis fabricated from a single material, such as photoresist. A monolithicmask avoids disadvantages associated with multi-layer masks, such asadditional processing steps.

Another embodiment of the present invention provides a method of usingan integrated mask to fabricate a passive matrix array of OLEDs.

FIG. 2 shows a cross sectional illustration of a mask 200 in accordancewith an embodiment of the invention. Mask 200 is disposed on a substrate210. Mask 200 has a central region 220 and an overhang 230. In centralregion 220, the mask material is in contact with underlying layers suchas substrate 210. The underlying layer may also comprise layers otherthan the substrate that have been previously fabricated. Overhang 230,by way of contrast, is not in contact with underlying layers. Instead,overhang 230 is separated from underlying layers by a recessed area 240in which mask material is not present. Mask 200 may be fabricatedentirely of a single layer of photoresist, avoiding the additional stepsand increased processing expenses associated with masks that includemultiple layers of photoresist and/or other materials.

Mask 200 has a total height represented by line 205, and a top widthrepresented by line 250. Central region 220 has a base width representedby line 270. Overhang 230 and recessed area 240 have a depth representedby line 260. At the outer edge of mask 200, overhang 230 has a thicknessrepresented by line 235, and recessed area 240 has a height representedby line 245.

Mask 200 is fabricated with an overhang having dimensions and aspectratios unprecedented in the prior art. One feature of the invention isthe “aspect ratio” of recessed area 240. This aspect ratio is defined asthe ratio of depth 260 to height 245. In an embodiment of the invention,the aspect ratio is at least 1.5. More preferably, the aspect ratio isat least 2.0. Most preferably, the aspect ratio is at least 2.2. It isbelieved that these aspect ratios are sufficiently large to minimize thedeposition of electrode material into the depths of recessed area 240 tothe point that there is no substantial conductivity across mask 200 dueto such electrode material.

In one embodiment of the invention, recessed area 240 preferably has adepth 260 of about 9.5 microns to 13.5 microns, more preferably about 11to 12 microns, and most preferably about 11.5 microns. Larger depths mayresult in an overhang that is not rigidly supported, and smaller depthsmay reduce the functionality of the overhang. The height 245 of recessedarea 240 may be about 2 to 6 microns, more preferably about 3 to 5microns, and most preferably about 4 microns. Lower heights may resultin the overhang undesirably touching the substrate at points, or in theoverhang coming so close to the substrate that a subsequently depositedlayer may undesirably bridge the gap between the overhang and thesubstrate. Higher heights may reduce the functionality of the overhangby allowing subsequently deposited material to readily enter too deeplyinto the depths of recessed area 240. However, depending upon theparticular process that is used to subsequently deposit material,dimensions outside of these preferred ranges may be used. Central region120 preferably has a width of about 5-9 microns, more preferably about6-8 microns, and most preferably about 7 microns. Smaller widths mayresult in a structurally unstable mask. Larger widths may result in themask having an undesirably large footprint. However, for applicationswhere mask footprint is not critical, larger widths may be readily used.

In one embodiment of the invention, mask 200 does not have a “foot.” Afoot is a region of the mask near the underlying layer where the centralregion becomes wider as it nears the underlying layer. For example, FIG.1 illustrates a mask 110 having a foot. By way of contrast, mask 200 ofFIG. 2 does not have a foot, because central region 220 becomes narroweras it nears underlying substrate 210.

In some embodiments of the invention, it is desirable to use planarizingor encapsulation techniques after mask 200 has been used to fabricate adevice. Many of the conventional planarizing or encapsulating techniqueswork best when applied to a device having height variation of less thanabout 3.0 microns, and more preferably less than about 1.5 microns. Itis therefore desirable in some embodiments of the invention to keep thetotal height 205 less than about 2.5 microns, and more preferably lessthan about 1.5 microns.

FIG. 3 shows a cross sectional photograph of an actual mask fabricatedin accordance with the present invention, similar to the maskschematically illustrated in FIG. 2.

FIG. 4 shows a cross sectional illustration of a device 400incorporating an integrated mask 450 in accordance with an embodiment ofthe present invention. Device 400 may be fabricated as follows. A firstelectrode 420 is deposited and patterned onto a substrate 410 usingconventional techniques. First electrode 420 and substrate 410 may bemade of conventional materials having conventional dimensions. If device400 is a top-emitting OLED, first electrode 420 and substrate 410 arepreferably selected to maximize back reflection.

An insulating strip 430 is then fabricated using conventionaltechniques. Insulating strip may be made of any suitablenon-electrically conducting material, such as SiN_(x), Al₂O₃,photoresist, or polyimide, and is preferably at least about 1000 Åthick, such that insulating strip electrically reliably insulates firstelectrode 420 from bus line 440. The width of insulating strip 430depends upon the type of device manufactured. For a passive matrixdisplay manufactured using presently available equipment, the array mayhave a pitch of about 50-400 microns. Subsequent technologicaldevelopments may enable a broader range of pitches. Preferably, theinsulating strip has a width that is about 10 to 45 percent of thepitch, and more preferably about 20 to 30 percent of the pitch. Asmaller width may not adequately separate adjacent pixels. A largerwidth may unnecessarily increase the inactive area of the array with acorresponding undesirable decrease in fill-factor. It is desirable tomaximize the fill-factor, or the percentage of the area of an emissivearray that actually emits light. In the embodiment of FIG. 4, thefill-factor is the percentage of the area not covered by insulatingstrip 430. In other embodiments, other features may further reducefill-factor.

A bus line 440 is then fabricated over insulating strip 430 usingconventional techniques. Bus line 440 may be made of any suitable metalor other electrically conductive material, such as gold, silver,aluminum or copper, or any suitable alloy. The dimensions of bus line440 are preferably chosen such that bus line 440 has a resistivityappropriate for the device being fabricated. The appropriate resistivityis generally based on the overall size of the display, and may bereadily determined by one of skill in the art. For example, in oneembodiment, a resistivity of about 0.3 ohms per square is preferred fora 2 inch square display with 80 dots per inch (dpi). A resistivity thatis too large may reduce the usefulness of the bus line, although anyresistivity significantly lower than that of second electrode 470 has atleast some usefulness. A resistivity that is too small may not result inany additional functionality, and may require an unnecessarily large busline 440.

A mask 450 is then fabricated over insulating strip 430 and bus line440, having dimensions consistent with the embodiment of FIG. 2. Mask450 is fabricated such that a portion of bus line 440 remains exposedvis-a-vis the insulating strip and the integrated mask, so that asubsequently deposited second electrode 470 may be electricallyconnected to bus line 440. Mask 450 is preferably fabricated such thatonly one side of bus line 440 is exposed, such that the secondelectrodes 440 of two adjacent devices 400 separated by mask 450 may notcontact the same bus line 440.

One or more organic layers 460 are then deposited through mask 450, suchthat organic layers 460 are electrically connected to first electrode420. Two layers can be “electrically connected” without being inphysical contact. For example, an intermediate layer, such as aninjection enhancement layer, may be present between an electrode and anorganic layer that are electrically connected. Organic layers 460 mayinclude any conventional OLED organic materials. Organic layers 460 maybe a single layer, or may include the multiple layers of conventionalOLED structures, such as a single or double heterostructure, or one ormore layers containing a mixture of OLED organic materials.

A second electrode 470 is then deposited through mask 450 and overorganic layers 460, such that second electrode is electrically connectedto organic layers 460. The dimensions of mask 450 allow second electrode470 to be fabricated without bridging across mask 450, using processesthat would lead to bridging across a conventional mask. Second electrode470 may be, for example, a sputter deposited electrode made of ITO,aluminum, or LiF:Al. These materials and other may be advantageouslyused to fabricate a very thin second electrode 470 which is transparent,such that light emitted from organic layer 460 may pass through secondelectrode 470 to a viewer, in which case device 400 would be atop-emitting OLED.

Note that residual organic and metal layers (not shown) are deposited ontop of mask 450 during the deposition of organic layers 460 and secondelectrode 470, respectively.

Organic layers 460 and second electrode 470 are deposited such thatsecond electrode 470 makes electrical contact with bus line 440, withoutsignificant interference from organic layers 460. In order to achievethis electrical contact, second electrode 470 should extend past organiclayers 460 onto bus line 440. This extension may occur because secondelectrode 470 is deposited using a technique that is less unidirectionalthan that used to deposit organic layers 460. Various processparameters, such as angle of deposition, may also be controlled toensure that second electrode 470 makes electrical contact with bus line440.

Depositing bus line 440 over insulating strip 430 advantageously avoidsthe creation of any additional inactive area on substrate 410. Using thedevice configuration shown in FIGS. 4 and 5, it is expected that a“fill-factor” or active area of at least 70% should be possible.

Mask 450 is preferably deposited over bus line 440 such that one side ofbus line 440 is completely covered by mask 450. This complete coverageon one side prevents a second electrode from an adjacent device fromcontacting bus line 440.

In one embodiment of the invention, the top width of mask 450 ispreferably about 100 microns, and the width of insulating strip 430 ispreferably about 150 microns. Preferably, the ratio of the width ofinsulating strip 430 to the top width of mask 450 is about 1.5:1.Preferably, the width of bus line 440 is about 30-40 microns.Preferably, the outermost exposed edge of bus line 440 is within about10 microns of the edge of recess 455, i.e., preferably the distancerepresented by line 457 is about +10 microns to about −10 microns. Ifbus line 440 does not extend past recess 455, and is too far withinrecess 455, it may be difficult to achieve good electrical contactbetween bus line 440 and second electrode 470. It is understood that theinvention is not limited to these specific dimensions.

Device 400 emits light when a current is passed between first electrode420 and second electrode 470, through organic layer 460. Secondelectrode 470 is electrically connected to bus line 440, and current mayreach second electrode 470 through bus line 440, in addition to runningalong the length of second electrode 470.

Although FIG. 4 shows only a single device 400, the invention may beused with multiple devices 400.

FIG. 5 shows the device of FIG. 4 from a top view. FIG. 4 is a crosssection of FIG. 5 across line 4′. Mask 450 is not shown. Bus line 440 isdisposed on top of insulating strip 430, such that there is noelectrical contact between bus line 440 and underlying first electrode420. Bus line 440 allows current to pass readily in the direction ofsecond electrode 470, effectively lowering the resistance of secondelectrode 470.

The embodiment of FIGS. 4 and 5 is primarily intended for use as atop-emitting OLED, such that light is emitted through second electrode470. However, the embodiment may also be used as a regularbottom-emitting OLED, such that light is emitted through first electrode420 and substrate 410.

It is to be understood that the present invention may be used tofabricate much larger arrays of organic devices than those specificallydescribed herein. Although FIG. 5 shows a 1×2 array of devices, muchlarger arrays may be fabricated. Moreover, a multi-color display may befabricated by depositing various down-conversion layers known to theart, or using different organic materials in different devices. Forexample, down-conversion layers may be patterned such that threeadjacent individual devices 400—one with no down conversion layer thatemits blue, one with a blue-to-green down conversion layer that emitsgreen, and one with a blue-to-red down conversion layer that emitsred—form a single multi-color pixel. An array of these multi-colorpixels may be fabricated to form a multi-color display. A multi-colorarray may also be fabricated by a number of other methods, such as usingan array of white-emitting OLEDs in combination with color filters or adistributed Bragg reflector.

It is also to be understood that the present invention is not limited tothe specific passive-matrix embodiment illustrated in FIGS. 4 and 5, andmay be used to in a wide variety of other embodiments. For example, thepresent invention may be used to fabricate an active matrix display.Each device in an active matrix array generally has one electrode thatis individually controlled for that device using a transistor. The otherelectrode is generally shared with all of the devices in the array. Inone embodiment of the present invention, an integrated mask having thenovel dimensions disclosed herein may be used to enable the fabricationof an active matrix display having, for example, a common secondelectrode. Such an array would be similar in appearance to theembodiment of FIGS. 4 and 5, but the first electrode of each device(pixel) in the array would be individually controlled by thin filmtransistors embedded in the substrate. These first electrodes would notbe connected in rows or columns as they are in a passive matrix display.All of the devices in the array would share a common second electrode,similar in appearance to that of FIGS. 4 and 5. Although the integratedmask may locally separate the second electrode into strips, these stripscould be electrically connected to each other at the periphery of thearray. This approach advantageously allows the second electrode tobenefit from the bus lines embedded in the integrated mask, whileavoiding the problems associated with fabricating a bus line after thedelicate organic layer is present.

Flexible substrates have several advantages that may make thempreferable to other substrates in certain circumstances. First, flexiblesubstrates may be used to fabricate arrays that can be flexed during thelifetime of the array—for example, a display screen that may be rolledup for storage. Second, flexible substrates may be used to fabricatecurved displays by flexing the substrate once and fixing it inposition—for example, a display screen may be attached to the curvedwindshield of a car or the curved surface of a building. Third, flexiblesubstrates may enable the use of particular processes duringmanufacturing, irrespective of whether the array is to be flexedlater—for example, the substrate may be stored or processed on rollers.Fourth, flexible substrates may be advantageous for reasons unrelated tothe flexibility, such as cost, in which case the substrate may beinadvertently flexed during or after fabrication of the array of OLEDs.Flexible substrates may also be advantageous for other reasons. The term“flexible” as used herein means that the substrate may be bent such thatthe radius of curvature is 1 meter or less without snapping orsustaining other permanent damage. However, some applications may usesubstrates that may be bent to much smaller radii of curvature, forexample 5 mm, without sustaining damage.

Of the materials that are presently commercially available, preferredflexible substrates include polyethylene terephthalate (PET),poly-ethersulphone (PES), polycarbonate (PC), polyethylenenaphthalate(PEN) and polyimide (PI). Each of these materials has advantages anddisadvantages that are more fully described in Weaver et al. It isexpected that chemical companies will develop new materials that arebetter suited for use as a flexible substrate for the fabrication ofOLED displays. It is also expected that various embodiments of thepresent invention may be practiced with such substrates when they becomeavailable.

OLEDs are sensitive to environmental factors, and may rapidly degrade ifexposed to moisture or oxygen. Many of the preferred flexible substratesare permeable to moisture and oxygen, such that an OLED fabricatedthereon may have a reduced lifetime. In order to address this problem, abarrier layer is preferably deposited onto the flexible substrate priorto the fabrication of the OLED. A preferred barrier layer includesmultiple sublayers of a high density dielectric, for example SiO₂,Si_(x)N_(y), Al₂O₃, or indium-tin oxide (ITO), alternating withsublayers of a polymer. A preferred barrier layer is Barix®, availablefrom Vitex Systems, Inc. of Sunnyvale, Calif. It is believed that aBarix® barrier layer is made up of alternating sublayers of polyacrylateand Al₂O₃. Preferably, the barrier layer has a total thickness of about1 to 10 microns, and includes 1 to 10 sublayers of high densitydielectric and polymer layers. The barrier layer may also be used toplanarize the substrate, i. e., to fill in any variations in the surfaceto provide a planar surface on which to fabricate the OLEDs. Otherpreferred barrier layers are disclosed in U.S. Pat. Nos. 5,686,360,5,757,126, 5,771,562, 5,811,177 and 5,874,804, which are incorporated byreference.

Flexing a flexible substrate may cause the electrodes of the OLEDs tocrack, delaminate, fracture or otherwise sustain damage which canadversely affect device reliability. The flexible substrate itself mayalso be damaged. It is believed that such damage is caused by thestresses imposed on the electrodes and the substrate by such flexing. Itis also believed that the stresses are greater in larger electrodes, andfor smaller radii of curvature. Yet, it is often desirable to fabricateelectrodes that span the entire array of devices, and it may also bedesirable to flex the substrate to a small radius of curvature.

For example, the pixels of the passive matrix display are organized bycolumns and rows. Each device in a particular column share a common topelectrode, which forms a strip running the length of the array.Similarly, each device in a particular row shares a common bottomelectrode, which forms a strip running the length of the array in adirection perpendicular to that of the top electrodes. As a result, theelectrodes of a passive matrix display may be quite long—on a screenhaving a seventeen inch width, the electrodes corresponding to the rowsare about seventeen inches long, and are conventionally formed of asingle strip of a thin conductive metal or metal oxide. The terms “row”and “column” are used herein interchangeably to refer to a line ofpixels that spans an array, and do not require any particular directionor association with a top or bottom electrode.

By way of further example, the devices of a conventional active matrixdisplay generally share a common top (or bottom) electrode, and haveindividually controllable bottom (or top) electrodes. As a result, thetop (or bottom) electrode spans the entire length and width of thedisplay, and is conventionally formed of a single sheet of a thinconductive metal or oxide. As used herein, the term “bottom electrode”refers to the electrode which is closest to the substrate, and isgenerally the first electrode fabricated, and the term “top electrode”refers to the electrode which is furthest from the substrate, and isgenerally the last electrode fabricated.

In one embodiment of the invention, large electrodes are physicallyseparated into a group of smaller distinct pieces, where each pieceserves as an electrode or part of an electrode for one or more devices.A bus line is used to preserve the electrical continuity of the group ofsmaller distinct pieces, in order to preserve the functionality of theoriginal, larger electrode. The smaller electrode pieces are lesssusceptible to damage when the substrate is flexed. The bus line, whichis not subject to the same constraints as the electrode, may befabricated to withstand flexing better than the electrodes. For example,at least one electrode of an OLED is generally transparent, which meansthat the electrode must be very thin and fabricated from particularmaterials, which may make the electrode susceptible to damage whenflexed. By way of contrast, a bus line does not cover the entire activesurface of the device, and need not be transparent. As a result, the busline may be fabricated to a greater thickness and from a wider varietyof materials.

FIG. 6 shows a cross section of an OLED 600. The device is fabricated ona flexible substrate 610. A barrier layer 620 is deposited on substrate610 to block any moisture or oxygen that might permeate substrate 610. Abottom electrode 630, an organic layer 640, and a top electrode 650 aredeposited, in that order, over the barrier layer. Preferably, at leastone of the electrodes, bottom electrode 630 or top electrode 650, istransparent such that light may pass through the electrode from organiclayer 640 to a viewer. However, some OLED applications may involveside-emitting OLEDs, in which case both electrodes may benon-transparent. Although the electrodes, organic layer and barrierlayer are described and illustrated as single layers, they may eachinclude various sublayers as known to the art. For example, the organiclayer may include the sublayers of a single or double heterostructureOLED, as described in U.S. Pat. No. 5,707,745, which is incorporatedherein by reference. In addition, device 600 may include additionallayers known to the art that are not illustrated, such as a holeinjection enhancement layer or a protective top layer.

The transparent electrodes, if any, of an OLED are preferably fabricatedfrom a conductive metal oxide. Preferred materials include indium tinoxide. Preferred non-transparent electrode materials include LiF:Al.Conductive polymers such as polyaniline and poly(3,4-ethylenedioxythiophene)/poly (styrenesulphonate) (PEDOT/PS) mayalso be used.

FIG. 7 (prior art) shows a top view of a schematic diagram of a passivematrix display 700. Bottom electrodes 720, a blanket organic layer (notshown to allow better illustration of bottom electrodes 720), and topelectrodes 730 have been deposited on substrate 710, in that order. FIG.7 illustrates four bottom electrodes 720, each of which spans the lengthof substrate 710 in the horizontal direction. Similarly, the five topelectrodes 730 each span the length of substrate 710 in the verticaldirection. Pixels 740 are defined by the regions where bottom electrodes720 and top electrodes 730 overlap, with the organic layer in between.FIG. 7 illustrates a 5×4 array of pixels 740, although only one islabeled. In a conventional passive matrix OLED display, substrate 710 isan inflexible material such as glass, ceramic or Si, which provides astable base for the display and acts as a barrier to moisture andoxygen.

FIG. 8 shows a top view of electrodes 805 fabricated on a substrate 810.FIG. 8 illustrates four electrodes 805, each of which spans the lengthof substrate 810 in the horizontal direction. Electrodes 805 includephysically separate pieces 820. The physically separate pieces 820 ofeach electrode 805 are electrically connected by bus lines 830.Electrodes 805 may be used, for example, to fabricate a passive matrixdisplay similar to that of FIG. 7 on a flexible substrate, whereelectrodes 805 replace bottom electrodes 720 of FIG. 7 to avoidundesirable cracking of bottom electrodes 720 due to the flexing orother stressing of substrate 710.

For example, an 80 dots per inch (dpi) passive matrix display could befabricated using the structure illustrated in FIG. 8. In one example ofsuch a display, physically separate pieces 820 are 280 microns by 280microns, and are separated from the other physically separate pieces 820by 40 microns on all sides. Bus lines 830 have a width of 40 microns. Inanother example of such a display, physically separate pieces 820 are260 microns by 260 microns, and are separated from the other physicallyseparate pieces 820 by 60 microns on all sides. Bus lines 830 have awidth of 40 microns. In yet another example of such a display,physically separate pieces 820 are 300 microns by 300 microns, and areseparated from the other physically separate pieces 820 by 20 microns onall sides. Bus lines 830 have a width of 40 microns.

By way of further example, a 60 dots per inch (dpi) passive matrixdisplay could be fabricated using the structure illustrated in FIG. 8.In one example of such a display, physically separate pieces 820 are 380microns by 380 microns, and are separated from the other physicallyseparate pieces 820 by 40 microns on all sides. Bus lines 830 have awidth of 40 microns.

In each of these examples, physically separate pieces 820 extendslightly under the bus line 830 to which it is electrically connected,such that there is no electrical contact between a physically separatepiece 820 and the bus line 830 of an adjacent electrode 805.

A conventional passive matrix OLED display, such as that illustrated inFIG. 7, has been strained to about 3-4%. While there was a negligibleeffect on device performance, similar experiments performed on rows ofITO lined with metal bus lines revealed significant cracking in both theITO and bus line regions. It is expected that such cracking could leadto reliability problems, particularly over the long lifetime that isrequired of display devices. The examples of dimensions that could beused to fabricate the structure of FIG. 8 are preferred dimensions thatare expected to mitigate cracking at pixel dimensions that are presentlycommercially desirable. However, the invention may be practiced with amuch wider range of dimensions.

FIG. 9 (prior art) shows a top view of a large, physically contiguouselectrode 905 fabricated on a substrate 910. Electrode 905 would besuitable, for example, for use as the common electrode of a conventionalactive matrix display.

FIG. 10 shows a top view of an electrode 1005 fabricated on a substrate1010. Electrode 1005 includes physically separate pieces 1020. Thephysically separate pieces 1020 of electrode 1005 are electricallyconnected by bus lines 1030 and 1040. As a result, electrode 1005 coversmost of substrate 1000. Electrode 1005 may be used, for example, toreplace a large physically contiguous electrode that spans an entireactive matrix display, such as electrode 905 of FIG. 9, to avoidundesirable cracking of such a large electrode when the substrate isflexed or otherwise subjected to stress.

In one embodiment of the invention, large electrodes that may besusceptible to cracking are not separated into smaller pieces to avoidsuch cracking. Instead, bus lines are used to reinforce the electricalconnection between different regions of the large electrode. If theelectrode cracks, current could still flow unimpeded through the buslines to all regions of the electrode.

FIG. 11 shows a top view of a physically contiguous electrode 1105 thatcovers most of substrate 1110. For example, electrode 1105 would besuitable for use as the common electrode shared by all devices of anactive matrix display. Bus lines 1130 and 1140 are disposed over, andare electrically connected to, electrode 1105. In the event thatelectrode 1105 cracks, current may flow through bus lines 1130 and 1140past the crack. Depending upon the flexing or other stress that isexpected to be put on electrode 105, a variety of bus lineconfigurations may be used. For example, bus lines 1140 may be omittedif any cracking is expected to be parallel to bus lines 1140.

FIG. 12 shows a top view of physically contiguous electrodes 1220 thatspan the length of substrate 1210 in one direction, but are relativelynarrow in the other direction. Bus lines 1230 are disposed over, and areelectrically connected to, electrodes 1220. In the event that electrodes1220 cracks, current may flow through bus lines 1230 past the crack.Because of the small dimension of electrodes 1220 in a directionperpendicular to bus lines 1230, it is likely that any cracking wouldoccur approximately perpendicular to bus lines 1230, and not parallel tobus lines 1230. Electrodes 1220 may be used, for example, to fabricate apassive matrix display similar to that of FIG. 7 on a flexiblesubstrate, where electrodes 1220 replace bottom electrodes 720 of FIG. 7to mitigate any undesirable cracking of bottom electrodes 720 due to theflexing of substrate 710.

In an embodiment of the invention, electrodes having physically separatepieces may be used in the individual devices of an OLED display in avariety of ways. For example, each physically separate piece of theelectrode may correspond to exactly one device. With reference to FIG.10, for example, if a single device is fabricated over each physicallyseparate piece 1020, then this one-to-one correspondence is established.

In an embodiment of the invention, each device may include a pluralityof physically separate pieces of an electrode. FIG. 13 shows a commonelectrode 1305 similar to common electrode 1005 of FIG. 10. Substrate1310, physically separate pieces 1320, bus lines 1330, and bus lines1340 of FIG. 13 correspond to substrate 1010, physically separate pieces1020, bus lines 1030, and bus lines 1040, respectively, of FIG. 10.Through appropriate placement of the other electrodes and organic layersusing conventional knowledge, devices 1350 may be defined. Each device1350 includes a plurality, four in this example, of the physicallyseparate pieces of electrode 1305. The embodiment of FIG. 13 may beuseful, for example, where a physically contiguous electrode as large asthe pixel would be susceptible to cracking.

In an embodiment of the invention, each physically separate piece of anelectrode may be a part of multiple devices. FIG. 14 shows a commonelectrode 1405 similar to common electrode 905 of FIG. 9. Substrate1410, physically separate pieces 1420, bus lines 1430, and bus lines1440 of FIG. 14 correspond to substrate 1010, physically separate pieces1020, bus lines 1030, and bus lines 1040, respectively, of FIG. 10.Through appropriate placement of the other electrodes and organic layersusing conventional knowledge, devices 1450 may be defined. A pluralityof devices 1450, four in this example, share each of the physicallyseparate pieces of electrode 1405. Even though each physically separatepiece 1420 may support several devices 1450, the devices are shown ononly one physically separate piece 1420 for clarity of illustration. Theembodiment of FIG. 14 may be useful, for example, where the size atwhich a physically contiguous electrode becomes susceptible to crackingis larger than the size of an individual pixel, but smaller than thesize of the array.

In an embodiment of the invention, the various electrode configurationsdescribed above with respect to flexible substrates may also befabricated on rigid substrates. The advantageous properties conveyed bythe electrode configurations may be useful for displays fabricated onrigid substrates in a number of circumstances. For example, thermalcycling of the display may lead to reliability problems if thecoefficient of thermal expansion of the substrate differs significantlyfrom that of the various layers in the device, such as the electrodes.Separating the electrodes into physically separate pieces may alleviatethis problem.

Although many of the embodiments show a bottom electrode havingphysically separate pieces that are electrically connected by a busline, the invention may also be practiced on a top electrode. Althoughit is expected that the mechanisms that lead to the cracking or otherfailure of a top electrode may differ from those that lead to thecracking or other failure of a bottom electrode, the division of the topelectrode into smaller, physically separate pieces may be useful. Forexample, many active matrix displays have a common top electrode, andthe present invention may be used to separate such an electrode intophysically separate pieces. Similarly, in a stacked OLED having morethan two electrodes per stacked device, the invention may be practicedon any or all of the electrodes.

Although many of the embodiments are not specifically described withrespect to multicolor displays, it is understood that all embodimentsmay be readily adapted for use in a multicolor display by one ofordinary skill in the art.

Although many embodiments illustrate a bus line deposited over anelectrode, the invention is not limited to such a configuration. Forexample, the electrode may be deposited over the bus line.

The present invention may be used to fabricate a number of products,including flat panel displays, photodetectors and transistors. Thepresent invention may be used to fabricate opto-electronic devices aswell, such as arrays of photovoltaic cells or photodiodes.

EXAMPLES

Photoresist masks having an overhang consistent with the presentinvention were fabricated using the following technique.

NR7-6000-PY photoresist was obtained from Futurexx, located in Franklin,N.J. Although the exact formulation of this photoresist is not known tothe inventors, it was developed at their request and is presentlycommercially available. NR7-6000-PY is a negative photoresist, becausepatterning the photoresist involves selective exposure to ultravioletradiation, and the subsequent removal of the unexposed portions. The useof a negative resist is preferred for integrated masks, because negativeresists can be extensively baked to minimize subsequent outgassing. Suchoutgassing may damage the organic layers of an OLED, or other sensitivedevice features, thereby undesirably reducing the lifetime of the OLED.

The photoresist was spin deposited at 2000 RPM for about 40 seconds. Thephotoresist was then baked at 120° C. for 5 minutes. Next, thephotoresist was exposed to ultraviolet radiation from a high pressuremercury lamp operated at a power of 13.5 mW/cm², for 150 seconds througha mask, such that only the portions of the photoresist that were toremain after developing were exposed. Then, the photoresist was baked at100° C. for 5 minutes. The photoresist was then developed in RD6, adeveloper commercially available from Futurexx.

The resultant mask had an appearance similar to that of the maskillustrated in FIG. 2 and photographed in FIG. 3. The total width of themask, represented by line 250 in FIG. 2, was approximately the same asthe width of photoresist that was exposed to ultraviolet radiation.

While the present invention is described with respect to particularexamples and preferred embodiments, it is understood that the presentinvention is not limited to these examples and embodiments. Inparticular, the present invention is not limited to OLEDs, and may beapplied to a wide variety of electronic devices. In addition, withrespect to OLEDs, the present invention is not limited to the particularexamples and embodiments described. The present invention as claimedtherefore includes variations from the particular examples and preferredembodiments described herein, as will be apparent to one of skill in theart.

What is claimed is:
 1. An array of organic light emitting devices,comprising: a first electrode having a plurality of physically separatepieces; a bus line that electrically connects the plurality ofphysically separate pieces of the first electrode; a second electrode;an organic layer disposed between the first and second electrodes, theorganic layer being electrically connected to the second electrode, andthe organic layer being electrically connected to at least one of thephysically separate pieces of the first electrode; wherein an organiclight emitting device includes more than one of the plurality ofphysically separate pieces of the first electrode.
 2. The array of claim1, wherein the array is fabricated on a flexible substrate.
 3. An arrayof organic light emitting devices, comprising: a first electrode havinga plurality of physically separate pieces; a bus line that electricallyconnects the plurality of physically separate pieces of the firstelectrode; a second electrode; an organic layer disposed between thefirst and second electrodes, the organic layer being electricallyconnected to the second electrode, and the organic layer beingelectrically connected to at least one of the physically separate piecesof the first electrode; wherein a physically separate piece of the firstelectrode is shared by a plurality of organic light emitting devices. 4.The array of claim 3, wherein the first electrode is a bottom electrode.5. The array of claim 3, wherein the array is fabricated on a flexiblesubstrate.
 6. An array of organic light emitting devices, comprising: afirst electrode having a plurality of physically separate pieces; a busline that electrically connects the plurality of physically separatepieces of the first electrode; a second electrode; an organic layerdisposed between the first and second electrodes, the organic layerbeing electrically connected to the second electrode, and the organiclayer being electrically connected to at least one of the physicallyseparate pieces of the first electrode; wherein the first electrode is atop electrode.
 7. The array of claim 6, wherein the composition of thefirst electrode includes a conductive metal oxide.
 8. The array of claim7, wherein the conductive metal oxide is indium tin oxide.
 9. The arrayof claim 6, wherein the array of organic devices is an array of organiclight emitting devices.
 10. The array of claim 6, wherein the array oforganic devices is an array of photovoltaic cells.
 11. The array ofclaim 6, wherein the array of organic devices is an array oftransistors.
 12. The array of claim 6, wherein the array is an activematrix display, and wherein the first electrode is electricallyconnected to every organic light emitting device in the array.
 13. Thearray of claim 6, wherein the array is a passive matrix display, andwherein the display includes a plurality of first electrodes such thateach first electrode is connected to every pixel in a particular columnof the display.
 14. An array of organic light emitting devices,comprising: a first electrode having a plurality of physically separatepieces; a bus line that electrically connects the plurality ofphysically separate pieces of the first electrode; a second electrode;an organic layer disposed between the first and second electrodes, theorganic layer being electrically connected to the second electrode, andthe organic layer being electrically connected to at least one of thephysically separate pieces of the first electrode; wherein the array isfabricated on a flexible substrate; and wherein the substrate may bebent to a radius of curvature of 1 meter without sustaining damage. 15.The array of claim 14, wherein the substrate may be bent to a radius ofcurvature of 5 mm without sustaining damage.
 16. The array of claim 14,further comprising a barrier layer disposed between the substrate andthe array.
 17. The array of claim 16, wherein the barrier layer furthercomprises multiple sublayers of a high density dielectric materialalternating with layers of a polymer.
 18. An array of organic lightemitting devices, comprising: a first electrode having a plurality ofphysically separate pieces; a bus line that electrically connects theplurality of physically separate pieces of the first electrode; a secondelectrode; and an organic layer disposed between the first and secondelectrodes, the organic layer being electrically connected to the secondelectrode, and the organic layer being electrically connected to atleast one of the physically separate pieces of the first electrode;wherein the physically separate pieces have dimensions of about 260microns to about 300 microns.
 19. The array of claim 18, wherein thearray is fabricated on a flexible substrate.